GLScene "Earth" demo.

A small (code-wise) demo that features earth, with night and day
texture maps, atmospheric effects, an orbiting moon, the sun,
a stars background and optional constellation lines.

The only technical part lies with the atmospheric effect, which
is raytraced on key points, and then interpolated in between. 
Yes, the earth atmosphere's is much thinner, but a thicker 
atmosphere looks better :)

Requirements:
- Hardware accelerated graphics with OpenGL support
- multitexturing and ARB_texture_combine support for city lights
  (ie. recent drivers and GeForce/Radeon-class hardware)
- 64 MB video memory for high-resolution resources support 
  (optional, and 128 MB recommended for optimal performance)

Keys and Controls:
- Mouse left click : move around your target body
- Mouse wheel : move comera closer/farther
- Mouse right click : adjust focal length
- 'E' : center and target Earth
- 'M' : center and target Moon
- '0'..'9' : adjust the speed, from paused (0) to superfast (9)
- 'C' : toggle constellation lines visibility
- 'H' : loads high-resolution resources

The high resolution resources are intended for GeForce3 and higher
video cards, with 64 MB or more of video memory, they are available
for download in a separate package at:

https://sourceforge.net/project/showfiles.php?group_id=29749

they include 4096x2048 textures for earth (night & day),
2048x1024 texture for the moon and the hipparcos star database
(87000 stars, rather than the 9100 ones in the default Yale db).
High-resolution mode also turns on FSAA (if available).

Resources credits and links:
- Earth textures from the NASA Blue Marble project
  (http://earthobservatory.nasa.gov/Newsroom/BlueMarble/)
- Moon texture from... dunno. Some bits looks like shots
  from the Clementine mission, with some manual cleaning up.
- Star databases are the Yale Bright Stars Catalog 
  (http://amase.gsfc.nasa.gov/amase/MissionPages/YALEBSC.html)
  and the Hipparcos Catalog up to magnitude 9.0
  (http://astro.estec.esa.nl/Hipparcos/catalog.html)
- Constellation lines file comes from "Cartes du Ciel"/"SkyCharts"
  (http://skychart.sourceforge.net/index.php)

Known issues:
- antediluvian video boards may suffer *a lot* from the smoothed
  points used to render the stars, or smoothed lines used to render
  constellations, consider yourself warned. If too horrible, delete
  or rename 'Yale_BSC.stars' to prevent the stars from being loaded.
- if you get crashes or freezes with the high-resolution textures
  on a 64MB or less video card, consider clocking down your RAM or CPU 
  (underclocking), they can put a lot of strain on these during AGP 
  texturing.

Eric Grange 
& GLS Team